The thermoforming of articles is well known in the art. Machines can be made to make single parts or simultaneously make a plurality of parts in an x-y array. In general, either a single sheet or roll sheet stock of formable material is heated and fed to a forming station and then through the application of force to the softened material is formed into one or more articles. When a plurality of articles are formed at one time from roll stock, they are connected by a web, at least along the outer longitudinal edges of the feed material. The articles are then separated from one another and the web typically by cutting with a die. The web can then be recycled if desired. The separated articles can be stacked and transferred to a storage or use area.
One early form of such a machine was available from Packaging Industries, Inc. of Hyannis, Mass. It was available in two models, the E-44 and the E-65. Both utilized an extruder to form the feed sheet of material. The machines though were not in line machines. Once parts were formed, they were first moved laterally to one side or the other of the machine before being transferred to other processing stations. These machines utilized stackers and stack pickers, however, the stack pickers were complicated and expensive.
One problem, particularly in the production of low margin products is cost. Each different article or different array of articles requires different tooling for forming, cutting and stacking. This increases the capital investment by manufactures which then gets passed on, at least partially, in the cost of goods. It also requires storage area for the tools. Stacking of finished parts and movement of the stacked parts can be done manually, but that also increases cost and can cause worker dissatisfaction because of the repetitive nature of the work. Another problem is that stacking and stack removal tend to be the bottleneck in the production process slowing down the operation of the other processing stations. One solution to this was the above mentioned machines that utilized a pair of processing lines to take outfeed from the molding station. This also increased machine cost and hence product cost or loss of profit. While stackers have been improved and simplified reducing their cost, stack pickers have lagged. Each different array in a stacker needs a custom picker to accommodate the different x-y arrays of rows and columns and different product sizes and shapes. The main expense of such devices is in the drive elements for the individual picker elements. These drives have to date been complicated and thus expensive and sometimes lacked in reliability.
Thus, there is a need for an improved stack picker assembly and thermoforming machine.